This invention has as its object the use of new crosslinking compositions for polysaccharides, in particular scleroglucan. It also relates to the use of aqueous gels including these crosslinking compositions for the selective reduction of the production of water in oil- or gas-producing wells. They exhibit a particularly great advantage when the permeability of the formation treated in the vicinity of the wells is high and/or when the water produced is hot and/or salty, for example at a formation temperature of 70.degree. to 130.degree. C. and/or a salinity of the water produced at least equal to that of sea water (at least 30 g/l, expressed in NaCl). These new compositions are particularly applicable to the enhanced recovery of hydrocarbons.
The recovery of the liquid or gaseous hydrocarbons of subterranean formations is very frequently accompanied by the production of large quantities of water. In some cases, although significant productions of hydrocarbons are obtained, the production of water is so considerable and the costs for treating the water so high that the production of hydrocarbons is not economical. In heterogeneous reservoirs, the excessive production of water is often caused by the fingering of the water injected through the zones of high permeability. This leads to a premature breakthrough of the water to the production well, to a poor volumetric sweep and finally to an ineffective recovery of the hydrocarbons.
Many methods intended to reduce the production of water of the very permeable formations have been proposed and tested in the field; they generally involve introducing into the formation, at the level of the zone to be isolated, either a cement or a suspension of solid particles or of paraffins. Resins or gels of water-soluble polymers have more recently been proposed and put into use. All these processes exhibit the disadvantage of not being selective and of blocking the circulation of the oil or gas almost as much as that of the water.
More recently, the use of water-soluble polymers of high molecular weight in the absence of any crosslinking or coupling agent has been proposed, polymers which exhibit the advantage, relative to the preceding solutions and in particular those which use resins or gels of polymers, of reducing the circulation of the water without affecting the production of oil or gas in a troublesome way.
Among these water-soluble polymers, nonionic polysaccharides and in particular scleroglucan have proved particularly effective in reducing selectively the production of water of production wells while maintaining the production of hydrocarbons. Thus, U.S. Pat. No. 4,718,491 and patent application FR 89/1716 of the applicant recommend the use of different polysaccharides, and in particular of a scleroglucan, in the absence of any crosslinking or coupling additive, for the selective reduction of the permeability in the vicinity of an oil- or gas-producing well. If the preferred range of application of these polymers covers the productions of hot (up to 130.degree. C.) and Salty water, its effectiveness decreases when the permeability of the formation becomes high and in particular if it is greater than 1 Darcy.
French patent application 90/13385 describes a crosslinking composition comprising at least one water-soluble complex having a base of polyvalent metallic cation and of complexing organic acid of the cation able to crosslink a polysaccharide, in particular scleroglucan.
U.S. Pat. No. 4,647,312 furthermore recommends the use of scleroglucan complexes and a polyvalent metal ion such as titanium, zirconium and chromium for the production of fluids of very high viscosity and their use in enhanced recovery of oil. Although no mention is made in this patent of the ability of these gels to propagate in a subterranean formation, the increase in viscosity obtained shows that it is strong gels which should not have any selective character and therefore reduce the production of water as much as that of the hydrocarbons. In addition, it is suggested to use zirconium tetrachloride, but the latter exhibits the drawback of being insoluble in a water with a salinity close to that of seawater.